1. Technical Field
The invention relates to methods for manufacturing semiconductor devices, and semiconductor devices.
2. Related Art
In electrical products that have been considerably reduced in size and weight in recent years, such as liquid crystal panels and portable mobile terminals, IC chips stored inside their housings may generally be mounted on a wiring substrate in a film shape that can be readily bent by hand, for example. The wiring substrate may be formed from an insulating film base member, and wiring patterns formed on the base member, and is called a tape carrier or a flexible substrate. Also, products with IC chips mounted on a film-like wiring substrate are called tape carrier packages (TCP), chip on films (COF) and the like. Japanese Laid-open Patent Applications JP-A-2003-249592, JP-A-2004-235322, and JP-A-2000-269249 are examples of related art.
For example, in the step of connecting (in other words, bonding) bumps of an IC chip onto inner leads, high temperature and high pressure may also be applied to the film that is the base of the inner leads, such that tip portions of the inner leads may be peeled off the film, as described in paragraph [0008] with reference to FIG. 6B of the aforementioned Japanese Laid-open Patent Application JP-A-2003-249592.
The inner leads may be formed through, for example, forming a copper foil on the film, patterning the foil, and plating zinc (Sn) on the surface of the foil. If the tip portions of the inner leads are peeled off the film, copper may be exposed in the peeled surface of the tip portions. If a voltage is applied to the inner leads in this state, electromigration may occur at the peeled surface, and the copper may grow in unintended directions.
For example, when a negative bias voltage (−) is applied to the inner lead where copper is exposed at the peeled surface of the tip portion, as shown in FIG. 5, a reaction (Cu2++2e−→Cu) progresses at the peeled surface. Also, when a positive bias voltage (+) is applied to the inner lead where copper is exposed at the peeled surface of the tip portion, a reaction (Cu→Cu2++2e−) progresses at the peeled surface. When the electromigration progresses in this manner, copper that is a wiring member grows at the tip portion of the inner lead, as indicated by a broken line in FIG. 5. Then, the grown copper may form bridges to and become short-circuited with adjacent inner leads.
Also, circuit forming surfaces (i.e., active surfaces) including the bumps of the IC chip, and bonded surfaces between the bumps and the inner leads are generally sealed with resin or the like, but moisture would likely be condensed between the resin and the film. If moisture adheres to the exposed surface (i.e., peeled surface) of the copper, ionization of copper and diffusion of Cu2+ would more readily occur, such that the electromigration is further accelerated.